VATICAN CITY — On his first day as shepherd of the world's 1.2 billion Catholics, Pope Francis picked up his luggage at a Vatican hotel, personally thanked each member of the staff and even paid his own bill. Then, at his first Mass, he delivered a short, unscripted homily — in Italian, not the Latin of his predecessor — holding the cardinals who elected him responsible for keeping the church strong.

Pope for barely 12 hours, Francis brushed off years of tradition and formality Thursday with a remarkable break in style that sent a clear message that his papacy is poised to reject many of the trappings enjoyed by now-retired Benedict XVI.

That was hardly out of character for Francis. For years, as Cardinal Jorge Mario Bergoglio, the Argentine pastor took the bus to work, kissed the feet of AIDS patients and prayed with former prostitutes, eschewing the luxurious residence that would have been his due as archbishop of Buenos Aires.

But now he is pope — the first from the New World and the first Jesuit — and his style both personal and liturgical is in a global spotlight.

On his first day, he couldn't have signaled a greater contrast to Benedict, the German academic who was meek and generous in person but formal and traditional in public.

The differences played out Thursday in the Sistine Chapel as the 76-year-old Francis celebrated his first public Mass as pope.

Whereas Benedict read a three-page discourse in Latin, Francis had a far simpler message. Speaking off-the-cuff for 10 minutes in easy Italian, he said all Catholics must "build" the church and "walk" with the faith.

He urged priests to build their churches on solid foundations, warning: "What happens when children build sand castles on the beach? It all comes down."

"If we don't proclaim Jesus, we become a pitiful NGO, not the bride of the Lord," he said.

"When we walk without the cross, and when we preach about Christ without the cross, we are not disciples of the Lord. We are mundane. We are bishops, priests, cardinals, popes, but we are not disciples of the Lord."

The new style was evident even in Francis' wardrobe. Rather than wear the new golden pectoral cross he was offered after his election Wednesday, he kept the simple crucifix of his days as bishop. He also turned down the red velvet cape that Benedict wore when he was presented to the world for the first time in 2005, choosing the simple white cassock of the papacy instead.

"It seems to me what is certain is it's a great change of style, which for us isn't a small thing," Sergio Rubin, Francis' authorized biographer, told The Associated Press.

Rubin said the new pope "believes the church has to go into the streets" and be one with the people it serves and not impose its message on a society that often doesn't want to hear it.

For this reason, as Cardinal Bergoglio, "he built altars and tents in the squares of Buenos Aires, and held Masses with former prostitutes and homeless people in the street," Rubin said. "He did this to express the closeness of the church to those who are suffering."

Rubin said he expected to see more changes — even substantive ones — once Francis gets his footing.

"I think the categories of progressive and conservative are insufficient," Rubin said. "Pope Francis is someone with a great mental openness to enter into dialogue. He is very understanding of different situations. He doesn't like to impose."

Francis began Thursday with an early morning trip in a simple Vatican car — not the papal sedan — to a Roman basilica dedicated to the Virgin Mary, where he prayed before an icon of the Madonna.

Like many Latin American Catholics, Francis has a particular devotion to the Virgin Mary, and his visit to the St. Mary Major basilica was a reflection of that. Laying flowers on the altar, he then prayed before a Byzantine icon of Mary and the infant Jesus.

"He has a great devotion to this icon of Mary, and every time he comes from Argentina he visits this basilica," said the Rev. Elio Montenero, who was present for the pope's arrival. "We were surprised today because he did not announce his visit."

Francis himself had foreshadowed the visit, telling the 100,000 people packed into rain-soaked St. Peter's Square after his election that he intended to pray to the Madonna "that she may watch over all of Rome."

The new pope, known for his work with the poor in Buenos Aires' slums, had charmed the crowd when he emerged on the loggia and greeted them with a simple and familiar: "Brothers and sisters, good evening."

On Thursday, members of his flock were charmed again when Francis stopped by the Vatican-owned residence where he stayed before the conclave to pick up his luggage. But that wasn't the only reason he made the detour.

"He wanted to thank the personnel, people who work in this house," said the Rev. Pawel Rytel-Andrianek, a guest at the residence. "He greeted them one by one, no rush, the whole staff, one by one."

Francis then paid his bill "to set a good example," Vatican spokesman the Rev. Federico Lombardi said.

"People say that he never in these 20 years asked for a (Vatican) car," Rytel-Andrianek said. "Even when he went to the conclave with a priest from his diocese, he just walked out to the main road, picked up a taxi and went to the conclave. So very simple for a future pope."

Francis displayed that same sense of humility immediately after his election, spurning the throne on an elevated platform that was brought out for him to receive the cardinals' pledges of obedience, said Cardinal Timothy Dolan of New York.

"He met with us on our own level," Dolan said.

Later, he traveled by bus back to the hotel along with the other cardinals, refusing the special sedan and security detail that he was offered.

Francis, said U.S. Cardinal Donald Wuerl, has signaled his adherence to a "Gospel of simplicity."

"He is by all accounts a very gentle but firm, very loving but fearless, a very pastoral and caring person ideal for the challenges today," Wuerl said.

Cardinal Thomas Collins, the archbishop of Toronto, agreed.

"He's just a very loving, wonderful guy. We just came to appreciate the tremendous gifts he has. He's much beloved in his diocese in Argentina. He has a great pastoral history of serving people," Collins said in a telephone interview.

And he has a sense of humor.

During dinner after his election on Wednesday, the cardinals toasted him, Dolan said. "Then he toasted us and said, 'May God forgive you for what you've done.'"